Air-backed thermistor bolometer



. 2,986,034 i 'Aranacrrsn rrmnsnsron BoLozvrcrnR United Patent 'O i 2 .Y device shown in Figs. 1 and 2, with the section taken approximate-.ly along the line 3-3 of Fig. 2;

Eig. 4- is a circuit diagram illustrating one manner in l which the thermistor bolometer may be used;

5 Fig. 5 is a plan'similar to Fig. 2 but illustrating a modi cation or' the device thereof, in which two separate ther- Robe? c' Jones' Cambmige Mass 35515105. by' meg" mistor elements or alres are mounted side by side, but ass'gnmentsthosthe Umdf tshmts of Amena as rep i separately, on insulation carried by the base, and illustratriienied e o. .e ing onemanner of establishing separate connections to the Filed Oct. 18,1957, Ser. No. 691,115 lo thermistor altes or elements; and

i Fig. 6 is a circuit diagram illustrating one manner in' 8 clams (CL v which the two thermistor flakes or elements may be conr nected in an operating circuit. 7

a In the embodiment of the invention illustratedy in Figs. Thisinvention relates to bolometers, and particularly 15 14 rile bOlOrDeer includes a CUPlilre housing 1 Whicbi to thermistor bolometers for measuring minte quantities normally closedby a cover 2 carrymga rrabSPare'll W111-A of radiant heat by changes in resistance in the thermistor dow 3 of a material that trarlsmlsdrlfrared. rays- Orl the strip or alre thatis exposed to the radiations. The ther-l boilom of tbe horrsrbgbcoealh lllevwmdow 3 1S Secured a mister is a resistor made of a material having a relatively base 4 of Subsidrllal 512e, and rrioarllcdon opposite ends high thermal coctiicient of resistance, whose resistance of .tbe toP of base 4 are rWo insulating blocks 5 and 5 varies greatly -with changes in temperature. Thermistors Willcb are fixed 111 Poslllorrrbereon- A rhcrmlsor element of this general type are well known in the art, several or balie- 7 exlerlds between the blocks 5 and 5 and rcSS being described f or example in.U.S. Patents No. 2,414,792 on tbc UPPer face hereof beneath rbc wlrrdoW 3- The and`No. 2,414,793.' -Thcrmistor resistors of this type that ends of the element 7 are Secured tothe bloelrs 5 and .65 are made from ceramiematerials are available in the open '171e 'blocl' 5 and 6 eXleHd Sllgllly hlgber than ille UPPer market and are sometimes calleda-ltes. Heretofore, the face of tbe base 4, S0 that ille element 7 will be spaced thermistor element or ake has commonly been supported Somewhat' from tbe UPPcr face of tbe base 4 The CUP' upon and in"s'7aced'relation to a face of the large block Shaped housing 1 arid Ils cover 2 are Preferably formed of nsulaaxial Such as glass and the ends of the o t' metallic silver, w1th the cover soldered .n closed posiake orthermistor element were cemented to the insulatbob 'libe Window 3 is Preferably made of Silver Chloride ing support or glass by a phenol-formaldehyde type of Wblcb 1S transparent; traasmlls mira-red, rays, arid can be resinous cement which required treatment under an elesoldered to lhecover 2 O vated temperature to cause the cement to set. This heat- The bare 4 1S Preferably made of all Iron-rilelel `alloy ing to set the cement caused considerable difficulty, be Sucb 'lrlvar or of a glass Scallbg alloy coDiaiD-Ulg about cause the glass' or other 'insulating material did not have 35 20% nickel, 17% Cobalt. 02% maDgarlcSe and the balthe same coeflcient of thermalexpansion as the thermistor arrcc iron" A11 alloy auch aS that laSr named iS malfelement or ilalte, and as a result-the thermistor element keted Under the trade ame Kol/ardy The rlVar is a 10W or Halte was often broken or damaged due to the unequal i thermal expansion nickel Sleel Particularly designed for expansion of the thermistor element and its support. rllerrbostalic clcmebrs- Each of these two alloys has An object of this invention is to provide an improved 40' aPPro'rirllalely ille Same' coefficient of thermal ex" thermistor bolometer in which a phenol-formaldehyde res` Parisiorl as tbe llicrmisror material@ Which iS Preferably inous cement may be employed successfully to attach the a ceramic material, and Since the base 4 and the thermisthermistor element-to the base or support, and to attach ylOl elem-Cnt 7 have the largest amounts of expansion, it the circuit wire leads to the ends of the thermistor eleiS POSSbl t0 Use Small blocks 5 and'6 of any insulating ment without danger of .breakage of, or damage to, the' 45 material, preferably of glass, since the thermistor elements thermistor element or the base, and without the thermistor at their ends can be secured to the glass blocks by a element becoming loosened from the support, and which PlleDOlrfOrmaldebyde reSirloUS Cement and ille reSiIlOllS will be relatively compact, durable, practical and inexcement set by heating.V rl`he blocks 5 and 6 are of pensive. f course secured or anchored in a suitable manner to the Another object of this invention is to provide an imbase 4. Suitable posts 8, Figs. 2 and 3, are' passed upproved thermistor bolometer of the airrbacked type which wardly through the bottom of the housing 1, and sealed may be easily andquickly assembled, and which may be therein by glass 9 as is common practice. The upper or enclosed in an air-tight capsule or housing, and which will inner ends of the postsl are connectedA one to each. end be relatively free from influence thereon of sound waves of the thermistor element 7 by lead wires 10. around the capsule or housing.

A circuit in which such a single thermistor` element Patented May 30, 1961 /Another object is to provide an improved thermistor,l may be used s illustrated in Fig. 4 where two sources ifbolometer which will be particularly sensitive to infra-redV of direct current 11 and 12, such as batteries, are .conradiation, which enables one to obtain and utilize radiation nected in series with each other by awire` 13. The bat- 3 from one source alone, and whichwill not give asignal -tery 11 in gonnected by wire 14 tio the lead 10 that is g if the radiation is from di'erent sources and ofie uall onn'cied fo one, end of the thermistor strip 7, and the Itfamountst. e other end of that thermistorstrip is connected by a wire 1S to one end of a resistance 16, such as a load re` sistanee, the other end of which is connected by a Wire 17 to the other battery 12,' which provides a closed cir` cuit in which the batterie, the thermistor element and y the yresistance are all connected in series. 'thermiStQr 'bolometer'constructed yin accordance with this b iap 1118 'lsdclzmetid ao the wir? 1st beiweer -tlhe inventionglhcsection being taken approximately along the a emes dm an, so comme e o grou une 1 11 Uf Fig 21 but with the cover in pl; 7? and an output lead 20 -1s connected to the wrre- 15 that Various other objects .and advantages will appear from the following-description of two embodiments ofA the invention, and the novel features will be particularly pointed out hereinafter in connection with the appended claims.

' 'In the'accompanying drawing:

Fig. 1- is a'longitudina'l sectional elevation through a Fig, 2 is a plan of the same before the cov is applied; connects one end of the thermistor element 7 to the r@ Fig. 3 is a sectional elevation through a portion of the sistance 1 6. With Such an arrangement 1f infra-red ra-g i t diation strikes the thermistor element 7 a plus signal ha ing a voltage dependent upon the intensity of-sueh radiation `is delivered to an external circuit through outputi Wire 20 and the ground connection 19. i

In the embodiment or the invention illustrated in Figs.

f and 6, the construction is the same as in Figs. 1 4,

except that the block 4 is made wider, the insulating blocks 5 and 6 are made longer, and two thermistor ele- .lation to one another.

ments 21 and 22 are mounted on the blocks 5 and 6 to extend therebetween, side by side, but in spaced re- In this embodiment four posts 23 extend upwardly through the bottom of the cup shaped housing part 1 and are sealed therein as in Figs. .l-3, and two of these postsare connected by wires 24 to 'the opposite ends of one thermistor. element 21' and the other two posts are connected by wires 25 to the opposite ends of the thermistor element 22.' Otherwise the con-'v struction is the same. as in Figs. l-3.

A suitable circuit for using the two thermistor elements is illustrated in Fig. 6, which is identical with the 'circuit shown in Fig. 4 except that the thermistor element 7 isreplaced by the thermistor element 21 and the resistance 16 is replaced by the thermistor element 22, and

parts similar to those in Figs. l4 are given the Asarne numerals. With this arrangement when the. infra-red radiations entering transparent window 3 strike one thermistor e'lement such as 21, a plus signal is delivered to the external circuit including wires 18 and 20. if the radiation strikes onlythc thermistor element 22, a negathermistor element or flake 7, 21 or 22, it is possible to use a phenol-formaldehyde type of cement to unite the thermistor element or ake to the base, because in heating the same to cause the cement to set, the approximately equal thermal expansion and constructionof the base and thermistor element or flake will result in no damage to the thermistor element. With this arrangement the glass insulating blocks at the ends of the base 4 may be used to facditate attachment of the ends of the thermistor elementto'the baseA because such pieces of glass are relatively short in the direction 'of thermal expansion and will not materially affect the normal thermal expansion and contraction of the base and thermistor element. Glass is particularly desirable as the insulating blocks because the cement will adhere thereto readily, and withstand the heating necessary to cause it to set. Hence, glassis preferred as the material of the insulating blocks, but other insulating blocks which will with stand the necessary heating may also be employed.

In this type of device it is important to have a ran'ed I atmosphere withinthe housing, because if there is much housing is preferably partially exhausted and the remaining air displaced by asmall amount of helium gas, such as will provide about2 mm. of pressure in the housing'. This has been found to eliminate any sound noises in the i It will be understood that various changes in the details,

the art within the principle and scope of the invention z' expressed in the appended claims.

I claim:

lorneteracomprising a closed housr -sgalattlagsitiiffrdny g, secured "to'hv' wllathll; and having an exposed face towards said window, sma electrically insulating blocks secured in spaced relatie to each other on said exposed face'of said base, a thermi tor-element extending between, xed to, 'andsupporte at its ends by said blocks in proximity to but spaced rel: tion to said base, electrically conducting leads extenda into said housing from the exterior thereof and electrical] thermal expansion as said thermistor element.

2. The 4thermistor bolometer, as set forth in claim and sa'idhousing containing a relatively small atmosphei i of helium gas and approximately free of air.

3. The thermistor bolornoeter, as set forth in claim I and said base being formed of a low thermal expansie alloy containing approximately 20% nickel, 17% cobal 0.2% manganese, and the balance iron.

4. The thermistor bolometer, as set forth in claim wherein said base is formed of a low thermal expansie alloy containing nickel and iron, said insulating blocl are formed of glass', and said thermistor element at i ends is cemented to said glass. f

5. The thermistor bolometer, .as set forth in claim wherein said base is formed of a low thermal expansic alloy containing nickel and iron, said insulating blocl materials and arrangement of parts, which have been herein described and illustrated in order to explain the are formed of glass, and said thermistor element at i ends is cemented to said' glass and said housing containit a relatively small atmosphere of helium gas and appro) mately free of air. z g;

6. The thermistor bolometer, as set forth in claim and a circuit having two sources of direct current co nected in series witheach other and with said thermist-I .elernent, a load resistance also in series with said eleme in said circuit, a ground connection to said circuit betwet said sources-of current, and an output electrical conne tion leading from arid connected to said circuit betwet said thermistor element and said resistance.

7. A thermistor bolometer comprising a closed housii having a transparent window that transmits infrared ra) a metallic base element in said housing and secured ther in to a housing wall with an exposed face of the eleme towards said window on which may fall infrared ra passing through said window, small blocks of electrical insulating material secured in pairs on said exposed fac the pairs being spaced apart, and the blocks of each pz being also spaced apart, a pair of thermistor elements, o: for each pair of blocks and extending between and tix 'to the blocks of that pair and in spaced relation to sa exposed face of said base, electrically conductingcirct leads extending into said housing and electrically co nected to said. thermistor elements, said base'having su stantially the same coeicient of thermaltexpansion said thermistor elements, said housing having a rar-ifi atmosphere containing a gas olering a minimum propel of transmission of soundwaves. i

8. The thermistor bolometer as set `forth inclaim' and a closed electric circuit having in series vthere two sources of electric direct current and said tt thermistor elements, a ground connection to the circt between said two sources of current and an output cc nection to the circuit between said thermistor elemen i References Cited in the file' of this UNITED STATE: Parnu-rs e f l www4' 1 OTHER REFERENCES I AAWide Range Thermstor Radio'znetcr, by Stoll 15x-1blished in Review of Scienfi Instrumexz,A vol. 25, No'. 2, Feb. 1954, pages 184,187.

Ail Evaporated Go in Journal o'f Scienti pages 24U-242.

Woolley et al. Mar.' 20, 1956 v 1d Bolometer, by Archbold publishedl c nstrumer'lts, voi.l 34, Jun=v1957, 

